Implementation:Ray project Ray Ray Get And Wait

Knowledge Sources	Ray Ray Objects
Domains	Distributed_Computing, Data_Transfer
Last Updated	2026-02-13 17:00 GMT

Overview

Concrete tool for retrieving distributed objects from the Ray object store provided by the Ray Java SDK.

Description

The Ray.get() and Ray.wait() static methods provide object retrieval from the distributed object store. Ray.get() blocks until the referenced object is available and returns the deserialized Java object. Ray.wait() returns a WaitResult containing lists of ready and unready object references, enabling efficient batch processing. Both methods delegate through AbstractRayRuntime to ObjectStore (backed by NativeObjectStore via JNI in cluster mode).

Usage

Use Ray.get() when you need the actual value of a computation result and are ready to block. Use Ray.wait() when processing multiple concurrent tasks and want to handle results as they arrive rather than waiting for all of them.

Code Reference

Source Location

• Repository: ray-project/ray
• File: java/api/src/main/java/io/ray/api/Ray.java (L86-173 for get/wait methods)
• File: java/api/src/main/java/io/ray/api/ObjectRef.java (L1-24, get interface)
• File: java/runtime/src/main/java/io/ray/runtime/object/ObjectStore.java (L1-259)

Signature

// Single object get
public static <T> T get(ObjectRef<T> objectRef)
public static <T> T get(ObjectRef<T> objectRef, long timeoutMs)

// Batch get
public static <T> List<T> get(List<ObjectRef<T>> objectList)
public static <T> List<T> get(List<ObjectRef<T>> objectList, long timeoutMs)

// Wait for readiness
public static <T> WaitResult<T> wait(
    List<ObjectRef<T>> waitList, int numReturns, int timeoutMs, boolean fetchLocal)
public static <T> WaitResult<T> wait(List<ObjectRef<T>> waitList, int numReturns, int timeoutMs)
public static <T> WaitResult<T> wait(List<ObjectRef<T>> waitList, int numReturns)
public static <T> WaitResult<T> wait(List<ObjectRef<T>> waitList)

// ObjectRef instance method
T ObjectRef.get()
T ObjectRef.get(long timeoutMs)

Import

import io.ray.api.Ray;
import io.ray.api.ObjectRef;
import io.ray.api.WaitResult;

I/O Contract

Inputs

Name	Type	Required	Description
objectRef	ObjectRef<T>	Yes	Future reference from a task submission
timeoutMs	long	No	Maximum wait time in milliseconds (default: Integer.MAX_VALUE)
numReturns	int	No (wait only)	Number of ready objects to wait for
fetchLocal	boolean	No (wait only)	If true, fetch object to local node before marking ready (default: true)

Outputs

Name	Type	Description
get() returns	T	The deserialized Java result object
wait() returns	WaitResult<T>	Contains ready (List<ObjectRef<T>>) and unready (List<ObjectRef<T>>)

Usage Examples

Blocking Get

import io.ray.api.Ray;
import io.ray.api.ObjectRef;

public class GetExample {
    public static int compute(int x) { return x * x; }

    public static void main(String[] args) {
        Ray.init();

        ObjectRef<Integer> ref = Ray.task(GetExample::compute, 7).remote();

        // Blocking get — waits until result is ready
        int result = Ray.get(ref);
        // Or equivalently: int result = ref.get();

        System.out.println(result); // 49
        Ray.shutdown();
    }
}

Wait for Multiple Results

import io.ray.api.Ray;
import io.ray.api.ObjectRef;
import io.ray.api.WaitResult;
import java.util.ArrayList;
import java.util.List;

public class WaitExample {
    public static int slowCompute(int x) {
        try { Thread.sleep(x * 1000); } catch (Exception e) {}
        return x;
    }

    public static void main(String[] args) {
        Ray.init();

        List<ObjectRef<Integer>> refs = new ArrayList<>();
        for (int i = 1; i <= 5; i++) {
            refs.add(Ray.task(WaitExample::slowCompute, i).remote());
        }

        // Wait for at least 2 results with a 3-second timeout
        WaitResult<Integer> result = Ray.wait(refs, 2, 3000);
        System.out.println("Ready: " + result.getReady().size());
        System.out.println("Unready: " + result.getUnready().size());

        Ray.shutdown();
    }
}

Related Pages

Implements Principle

• Principle:Ray_project_Ray_Object_Store_Retrieval

Requires Environment

• Environment:Ray_project_Ray_Java_Build_Environment